The invention relates to response time testing of nuclear power plant equipment, and in particular to the measurement of elapsed time between the occurrence of a plurality of associated, physically separated, or electrically isolated events.
Response time is the elapsed time between the occurrence of an initiating event and a dependent event in which the dependent event occurs in response to the initiating event. For example, the elapsed time between when an operator intiates the closing of a valve by changing the position of a switch in the control room and the time the closed limit switch on the valve indicates the valve has closed. Response time can involve more than two associated events. A single initiating event may have more than one associated dependent event; a dependent event may be the initiating event for a subsequent dependent event. It may be desired to know when the pressure downstream of the valve has decreased to a desired level relative to when the operator initiated closing the valve or relative to when the valve was proven closed by the close limit switch. Response time testing is the determination of the elapsed time between the occurrence of the associated events.
Existing timers generally measure the elapsed time between a start signal and a stop signal. The start and stop signals may be mechanically or electrically intiated. When they are electrically initiated, the electrical start and stop signals are measured relative to a common ground and are wired back to the timer at a single location.
Response time testing can be performed using conventional timers by starting two conventional timers simultaneously and then stopping them by physically separated or isolated events. The first timer would stop timing upon the occurrence of the initiating event; the second timer would stop timing upon the occurrence of the dependent event. The difference in elapsed time between the two timers is the response time. There is, however, no way to time additional pairs of events while the timers are separated. The timers must be taken back to a common location and again simultaneously started to perform another response time test. Alternatively, a pair of electrical conductors can be taken with each timer to accommodate simultaneously restarting the timers after one response time test in preparation for another response time test. Either of these alternatives becomes cumbersome when response time testing the many pieces of equipment in preparation for plant startup of a nuclear power plant.